Anilox

In printing, anilox is a method used to provide a measured amount of ink to a flexo printing plate.

An anilox roll is a hard cylinder, usually constructed of a steel or aluminum core which is coated by an industrial ceramic whose surface contains millions of very fine dimples, known as cells. Depending on the design of the printing press, the anilox roll is either semi-submersed in the ink fountain, or comes into contact with a so-called "metering roller" which is semi-submersed in the ink fountain. In either instance, a thick layer of typically viscous ink is deposited on the roll. A razor-sharp 'doctor blade' is used to scrape excess ink from the surface leaving just the measured amount of ink in the cells. The roll then rotates to contact with the flexographic printing plate which receives the ink from the cells for transfer to the printed material.

The characteristics of an anilox roll determine the amount of ink that will be transferred to the plate: angle of the cells, cell volume, and line screen. A 60% angle ensures maximum density in a given space. Lower volume makes for less ink. Low line numbers will allow for a heavy layer of ink to be printed, whereas high volume will permit finer detail in printing. Both cell volume and line screen are closely correlated.

Anilox rolls are often specified by their "line screen", or, the number of cells per linear inch. These often range from around 250 to upwards of 1500, though the precise numbers vary by manufacturer. Anilox rolls are almost always designed to be removed from the press for cleaning and for swap out with different line screen rolls. Depending on the detail of the images to be printed, the press operator will select an anilox roll with a higher or lower line screen. Low line screen rolls are used where a heavy layer of ink is desired, such as in heavy block lettering. Higher line screens produce finer details and are used in four-color process work such as reproducing photographs. Often a job will require a different line screen for each color to be printed. Experienced press operators are skilled at determining the appropriate anilox rolls for a given print job.

Though large wide-web flexo rolls are only maneuverable by overhead crane, on smaller presses anilox rolls are often handled directly by operators. Extreme caution must be taken when handling these pieces of hardware as a single bump against a hard surface or sharp corner can destroy the delicate cell structure on the surface and render a roller completely useless. At a cost of around USD 5000 for even small narrow-web rollers, nicks and scratches add up quickly. Similarly, anilox rollers that are used with water and oil based inks, which dry when left sitting out and unagitated, must be cleaned immediately after use or a problem known as "plugging" occurs where minuscule amounts of ink dry in the cells. This leaves tiny, but unacceptable, pinholes in anything printed from the roll in the future.

Anilox rolls were originally made using a diamond pecking machine, but modern rolls are laser engraved.